Melt spinning apparatus

ABSTRACT

In a melt spinning apparatus, cooling system with a blower nozzle with slit-shaped outlet openings is used which is directed upon the yarns emerging from the spinning nozzle. The blower nozzle is provided with a bend immediately before its outlet opening through which the air stream is directed to the output of the yarns from the spinning nozzles. The bend is designed so that a rapid and effective cooling of all the extruded filaments takes place, even with a nozzle package with a large number of perforations, without having to provide several blower nozzles. A narrowing at a given distance before the outlet opening ensures even distribution of the flow profile produced over the entire outlet cross-section of the blower nozzle. Furthermore, the spinning nozzles are assigned an induction heating system in which induction coils are placed above the area over which the spinning nozzles extend.

This is a Continuation application of Ser. No. 08/758,641, filed Nov.27, 1996, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for the extrusion of amolten polymer material into a plurality of yarns, whereby thisapparatus is provided with distribution channels through which themolten mass is fed to spinning nozzles, as well as with heating devicesin order to keep the material flow at the required temperature forextrusion until emergence from the nozzle bores, and furthermore with acooling system with a blower nozzle associated with the nozzle boreshaving a slit-shaped outlet opening which is directed upon the yarnsemerging form the nozzle bores so that the latter are subjected to theair flow coming out of the blower nozzle.

Filaments of yarn-forming polymers such as polyester, polyamide andpolyolefine are normally produced in the melt-spinning process. In thisprocess, the polymer is melted down and homogenized in an extruder andis then fed through a melt line to spinning pumps which press the moltenmass through nozzle bores. The filaments emerging from the spinningnozzles are continuously cooled by an air stream. The filaments thusproduced are then prepared, gathered together into a cable, drafted,crimped and cut into staple fibers.

The first steps of the process have a great influence on the subsequentprocess steps with regard to product quality, so that even before orduring the yarn formation the final quality of the yarns or staplefibers is decidedly determined.

The process starts with the extrusion, which must deliver as homogenousa molten mass as possible with respect to temperature distribution, andif applicable, also distribution of additives.

The distribution of the molten mass among the nozzle bores takes placetherefore in precisely stepped channel system with as identical channellengths as possible for all spinning pumps. Constant temperature isensured by means of heating of all channel segments in as uniform amanner as possible. Gear pumps with frequency-regulated drives provideprecise dosage of the individual volume flows to the nozzle bores.

In practice, different shapes of the spinning nozzle packages, i.e.rectangular, annular and round-nozzle packages are used, depending onthe application, and for these as uniform a distribution of the moltenmass must ben ensured in turn over the entire output surface of themolten mass.

A distribution system of this type for a ring-nozzle package is shownfor example in EP 0 517 994, where the molten mass is conveyed through acomplicated system of channels of equal length to the nozzle bores of aring-shaped nozzle package. In U.S. Pat. No. 4,259,048 an annular nozzlepackage is described in which the distribution of the molten mass isensured by a plate-shaped space.

However, these solutions function faultlessly only if all the channelsare at the same temperature, as otherwise differences in the flowcapability of the polymer appear due to the temperature difference, andthe molten mass flows preferably through the warmer channels accordingto the principle of least resistance. This expresses itself clearly inthe difference in titer and is expressed in the end product through thevariation coefficient. Furthermore, such temperature irregularities havea detrimental influence upon draftability, so that high product qualitycannot readily be achieved. This applies in particular to the productionof very think fibers or filaments, since the inherent enthalpy is lower,due to the lower throughput, and therefore the influence of temperatureon the viscosity of the molten mass is greater because of the longerdwell time.

In practice it has been found however, that even in a housing heatedwith a vaporous heat-carrying oil with seats for the spinning nozzles,the so-called spinning beam, temperature differences occur because thenozzles cannot be installed without gaps. Gaps serve to compensate fordeformation processes when seals are crushed, or are required as safetyclearances because of the heat expansion occurring at the processtemperatures between 220 and 300° C. Because of these gaps, the optimalheat transfer through heat conduction can be used only to a very limitedextent.

The utilization of electrical heating elements (DE 4 312 309 C2) whichcan be screwed or clamped directly on the spinning nozzle package,offers a solution. This means however, that the energy required forheating must be supplied through wires and contacts which must beremoved when a spinning nozzle package or even parts of same must bedisassembled, and this considerably increases the cost and also leads toincreased wear of the parts involved. Furthermore, energy losses occurin the wires and contact bridges. Another aspect here is the danger tomachine operators due to electrical voltage which appears on theseheating elements and may endanger personnel in case of improperhandling.

The direct thermal oil heating system also represents a considerablecomplication in installation and removal of the spinning nozzles or ofthe nozzle package, since oil pollution can be expected during theestablishment or the removal of the connections. Furthermore theseresidues interfere with the cleaning of nozzle bores in cleaningdevices. Local temperature adaptation in case of interfering influencesis not possible.

The uniformity of yarn cooling at emergence from the spinning nozzlepackage has as much importance as even distribution of the molten mass.Here it must be ensured that each filament is cooled with the mostuniform air temperature possible on the same path and at the mostuniform speed possible. Cooling at the congealing point of the moltenmass is of the greatest importance here, since the momentary position ofthe still freely moving and already pre-oriented molecules of thesynthetic material is frozen. Differences in cooling result as a rule indifferences in draftability and, in the worst case, to yarn breakagealready in spinning. To reduce these influences, lateral blowing, inflowcooling (from the outside to the inside) and outflow cooling (from theinside to the outside) is applied, depending on the nozzle shape used.Depending on the density of the field of perforation, on the width ofthe field of perforation, on polymer and throughput, the air velocityvaries between 0.1 and over 20 m/s.

All cooling processes and air velocities have the common problem thatthe blown air heats up as it penetrates the filament group from filamentto filament and has therefore a distinctly higher temperature at itsoutput than on the input side. Consequently, the filaments on the outputside receive different cooling from the filaments on the input side ofthe cooling air. As described earlier, this leads to differences indraftability and to reduced product quality. In addition, the movementof the filaments and the resulting drag flow cause a certain amount ofdeflection of a previously well directed air stream, so that theuniformity of the congealing point between input and output side is alsono longer ensured.

EP 0 536 497 therefore describes a cooling system with outflow blowerswhich consist of two units with different orientation and withsubstantially independent adjustability with respect to blown air flowto reduce the temperature differences or to compensate for the blown airdeflection. This blown air stream is expensive and yet not satisfactory.

OBJECTS AND SUMMARY OF THE INVENTION

It is a principal object of the present invention to improve theconditions for the extrusion of the yarn-forming polymer materials andthereby the quality of the final product. Additional objects andadvantages of the invention will be set forth in part in the followingdescription, or may be obvious from the invention, or may be learnedthrough practice of the invention.

The objects are attained by the device according to the invention. Theblow nozzle according to the invention makes it possible to achieverapid and effective cooling of all extruded filaments in a uniformmanner, also with nozzle packages with a large number of perforations.Without having to provide several blowing nozzles, which wouldfurthermore have to be adjustable independently of each other for thecorrect cooling air amount and velocity, the correct distribution ofquantities and velocity through the configuration of the blower nozzleis achieved according to the invention. The surprisingly strong effectof this blower nozzle according to the invention is obviously due to thefact that due to the velocity distribution and the considerably highervelocities on the side of the blower nozzle away from the spinningnozzle package, an injector effect is produced which causes suction ofair away from the area below as well as from outside the filament group.This creates a circulation within the filament group, with the airsucked from the outside through the filament group acting as areinforcement of the blown air stream emerging from the blower nozzle.Due to the fact that the circulatory movement causes fresh air to beaspired from the outside to the inside, cool air first reaches the outerfilament flows and thereby leads to a further reduction of the coolingdifferences between the filament rows on the input side of blown air andthose on the output side of blown air. To increase the cooling capacity,spraying of water or a spinning solution into the flow of blown air isadvantageous. The evaporation of the fluid atomized into aerosols causeslarge amounts of heat to be withdrawn from the molten and flowingfilaments and causes a significant reduction of the cooling length untilthe molten mass congeals. Since the cooling capacity represents alimitation of throughput, in particular in the production of thickfilaments, the productivity of the spinning apparatus is therebyincreased considerably. The upstream bend in opposite direction to thebend at the nozzle output makes it possible to feed cooling air alsofrom below.

It has been shown that the uniformity of the air velocity over thecircumference of the blowing nozzle plays also a decisive role in thereliable running of the filament production. In spite of the mostprecise adjustment of the gap of the blower nozzle over the entirecircumference, defects in running reliability of filament production dooccur. Due to the fact that a narrowing precedes the outlet opening, inparticular the bend, through which the air stream is compressed andflattened, the air velocity is substantially evened out over the entireoutput area of the nozzle.

It has been shown that by using an induction heating system, a heatsource is made available which causes heat to be produced where it isneeded, i.e. in the nozzle package. In order to even out the heating, ashort-circuit ring can additionally be provided, in which current beginsto flow through induction and heats up said short-circuit ring. The heatis thus brought on the shortest way to the critical locations of thenozzle package, the distribution channels as well as the nozzle platewith the field of perforations, without cable and contact connections,or it is produced directly there, so that losses are avoided. Whenreplacing the nozzle package or parts thereof, only the mechanicalattachment of the nozzle package must be opened. The induction heatingsystem can remain as is in its place.

Additional details of the invention are described through the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overall view of the apparatus according to theinvention;

FIG. 2 shows the temperature increase when the air flows through thefilament group according to the state of the art;

FIG. 3 shows the distribution of flow velocity at the outlet of theblower nozzle;

FIG. 4 shows the circulation flow in combination with the blower nozzle;

FIG. 5 shows the adjusting device of the blower nozzle;

FIGS. 6 and 7 show the induction heating system schematically;

FIG. 8 shows the apparatus according to the invention, with blown airfed from above;

FIG. 9 shows another embodiment of the induction heating system;

FIGS. 10/11 show details of the embodiment of FIG. 9; and

FIGS. 12/13 show to additional embodiments of the design of the blowernozzle according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the presently preferredembodiments of the invention, one or more examples of which areillustrated in the drawings. Each example is provided by way ofexplanation of the invention, and not meant as a limitation of theinvention. For example, features illustrated or described as part of oneembodiment can be used on another embodiment to yield a still furtherembodiment. It is intended that the present invention cover suchmodifications and variations.

FIG. 1 shows an annular spinning nozzle package 1 which is built into ahousing 4 and contains nozzle bores 111. Out of the nozzle bores 111,correspondingly circular filaments 9 emerge and are drawn off viadraw-off roller 18. The filaments 9 are bundled by two preparationrollers 17 and 19 facing each other which are applying at the same timethe preparation liquid needed for further processing. Blown air L isdirected via a pipe 8 which is concentric with the spinning nozzlepackage 1 to a blower nozzle 70 which consists essentially of a lowerpart 6 and an upper part 7. The blown air emerges radially to theoutside from the outlet opening 16 and flows through the filaments 9from the inside out, immediately following their emergence from thenozzle bores 111. The outlet opening 16 of the blower nozzle 70 isannular in form to correspond to the circular arrangement of the nozzlebores 111 and is concentric with the spinning nozzle package 1.

The molten mass P is fed to the spinning nozzle package 1 by a spinningpump 5 which feeds the molten mass P via distribution channels 41 to thespinning nozzle package 1 and distributes them evenly. The uniformity oftemperature which is necessary for a good distribution of the moltenmass is ensured by means of an induction heating system with inductioncoils 3 with U-shaped iron core 32 and with a short circuit ring 2. Theshort circuit ring 2 is imbedded in a recess 21 (FIG. 7) in the spinningnozzle package 1 and is directly connected to the spinning nozzlepackage 1 through screwing or in a similar manner, so that the heatproduced in the short circuit ring is transferred directly to thespinning nozzle package 1. The induction coils 3 are distributed evenlyover the circumference of the short circuit ring . The U-shaped ironcore 32 installed in the spinning nozzle package 1 in the recess 21causes magnetic field lines M to be produced which flow through theferromagnetic material of the spinning nozzle package 1 in radialdirection (FIG. 7) when current flows through.

The spinning nozzle package 1, as well as the induction coils 3, arelocated in a housing 4 of the spinning apparatus, so that the spinningnozzle package 1 can be installed independently without affecting theinduction coils 3.

The air supply from below which is required because a centraldistribution of the molten mass is used is directed by a special blowernozzle 70 upon the filaments 9 emerging from the nozzle bores 111.

As can be seen in FIGS. 3-5, the blower nozzle 70 is designed in aspecial manner to guide the blown air stream L. The upper part 7 and thelower part 6 together constitute a guide for the air, whereby the airguide in the lower part 6 is provided with a bend 61 shortly before theheight adjustment threads 10 through which the air stream is deflectedto the output of the filaments 9 from the nozzle bores 111. The crest ofthe bend 61 is therefore on the side away from the nozzle bores 111. Asthe air flows through this bend 61 it is compacted at the outside of thebend 61 and as a result is given greater velocity at that point. Thisvelocity profile is shown schematically in FIG. 3. Depending on theconfiguration of the arc of this bend 61, it serves to obtain a velocityprofile that is advantageous for the flow through the filament bundle.

In tests it has now been shown that the following applies basically: Thesharper the deflection through bend 61 before the outlet opening 16 ofthe narrowing, the more distinct is the velocity profile. However thisalso increases the turbulence of the flow. It was furthermore found thatas the bend angle α increases, the height of the blower nozzle 70 alsoincreases, and this is not desirable, so that the bend angle α shouldpractically not be greater than 90°. Within this range, the constructiveheight of the blower nozzle 70 remains suitable, and a good and distinctflow profile without great turbulence is thus produced nevertheless.

Since the length of the segment after the bend 61 can reduce turbulencebut since the velocity profile produced by the deflection is then againrendered more uniform, a length equal to preferably twice to four timesthe height H of the cross-section of the outlet opening 16 has proven tobe optimal.

Measurements have shown that the production of such a flow velocityprofile of the blower nozzle 70 produces a circulatory flow Z whichassists and reinforces the cooling air stream of the blower nozzle 70 ina most advantageous fashion. In FIGS. 3-4 it can be seen that the airstream emerging from the outlet opening 16 exerts an injector action andsucks air from the area below the blower nozzle 70. This goes so farthat air follows even from the area outside the filament bundle 9 andthen exerts a cooling action upon the outer filaments 9 before beingused up. However an air circulation Z also takes place inside thefilament bundle 9 due to the downward movement of the filaments. Thisapparently explains the great effectiveness of the blower nozzle 70 madeaccording to the invention.

The cooling action of the blown air L can of course also be reinforcedby injecting water or a spinning preparation. For this purpose, spraynozzles 81 can be provided either inside the blown air channel 8 and/orin star form around this blown air channel 8 (FIG. 4). Here too the aircirculation described above has a favorable effect.

In the described embodiment (FIGS. 1-4), the blown air stream L isdirected from below through the blown air channel 8 to the blower nozzle70. Since the blown air must blow from the inside out through thefilament bundle 9, a deflection of the air stream by about 90° isnecessary. Such a deflection would however produce an undesirable flowprofile. For this reason the bend 61 is preceded by a second bend 71,whereby its crest is located in the upper part 7 of the blower nozzle70. This upper part 7 extends in the form of a roof upward or, if theblower head is round, it is conical, so that sufficient space isprovided for the bend 71. These two bends 71 and 61 installed one afterthe other cause the air, which rises vertically, to be first deflecteddownward, to be then directed in such manner by the bend 61 with thedesired velocity profile at the outlet 16 that the blown air streamseizes the filaments 9 emerging from the nozzle bores 111 immediatelyover the entire width of the spinning nozzle package 1. The air flowemerging at the lower edge of the bend 61 reaches the filament bundle 9at a greater velocity here, and at a greater distance from the nozzleoutput, than the airstream arriving with slower speed at the inner wallof the bend 61 formed by the upper part 7, which reaches the yarn bundle9 immediately upon emergence from the nozzle bores 111 on the inputside, while the filament bundle 9 is subjected on the output side to thegreater air velocity on the outside of bend 61.

To be able to position the blower nozzle 70 in at a perpendicularrelative to the nozzle bores 111, it is equipped with a positioningdevice which also makes it possible to adjust the width of the outletopening 16. FIG. 5 shows this adjusting mechanism by means of which theblown air L can be adjusted precisely to the applicable requirements.The blower nozzle 70 is radially fixed by means of the centering device15 which is connected via the connecting rod 14 to the threaded segment11. By rotating the threaded segment 11 on the threads 10 at the end ofthe blown air channel 8, the height of the centering device 15 isadjusted and is introduced into a centering recess 42 of the housing 4(FIG. 1). The height of the upper part 7 of the blower nozzle 70 can nowbe adjusted so that the filaments 9 are cooled at the optimal momentafter coming out of the nozzle bores 111.

The position of the lower part of the blower nozzle 70 can be changedthrough the threaded segment 11 and the compensating segment 12. Bychanging the position of the lower part 6 relative to the upper part 7,the outlet opening 16 can be adjusted in this manner so that therequired cooling path up to the congealing of the filaments 9 isavailable for any titer, any material, and any production speed. Througha correct adjustment of the outlet opening 16 in combination with theconveyed mass of blown air L, it is possible to avoid an unnecessarilyhigh consumption in air while nevertheless achieving the requiredcooling effect. Especially when finer fibers are spun, where a verylarge number of perforations are provided in the spinning nozzle package1 for the sake of improved economy, the high air speeds necessary toovercome the resulting penetration resistance can be achieved byreducing the outlet opening 16 in this manner.

For an even cooling of the filaments 9 extruded from the nozzle bores111, not only the described flow profile is necessary, but also that theflow profile be evenly present over the entire outlet opening of theblower nozzle. Even with the most precise adjustment of the gaps of theblower nozzle over the entire circumference, defects in the runningreliability of the filament production may otherwise occur. FIG. 12shows a blower nozzle head similar to the FIGS. 1, 3 and 4 which havealready been described.

In FIG. 12 the blower nozzle 700 consists of an upper part 707 and alower part 706. The lower part 706 is connected to a blown air channel 8from which the blown air stream L enters the blower nozzle 700. Thenozzle 700 can be a ring nozzle, for example, where the blown air streamL enters centrally from below and flows from the center of the blowernozzle 700 to the ring-shaped outlet opening 716, where it leaves theblower nozzle 700 and flows against the filaments 9 emerging from thebores 111 (not shown) of the spinning nozzle 1. In this way the blownair stream L first passes a deflection 720 which is followed by anarrowing 705 and which is in turn followed by a bend 710 before theblown air stream L reaches the outlet opening 716. The narrowing isproduced by reducing the height h between the air guiding walls of theblower nozzle 700. The outlet opening 716 which follows the narrowing705 has however again a greater height H than the narrowing 705. Theblown air then emerges radially to the outside from the outlet opening716 and flows the filaments 9 (not shown here) directly after theiremergence from the nozzle bores, from the inside out. The outlet opening716 of the blower nozzle 700 is ring-shaped in conformity with thecircular arrangement of the nozzle bores and is concentric with thespinning nozzle package 1 (not shown here). As mentioned earlier, it hasa cross-section with a greater height than the narrowing 705. The blownair channel 8 has a cross-section at the intake into the blower nozzle700 that has again a greater height than the narrowing 705, so that thisnarrowing causes a deformation of the blown air stream L in such amanner that the latter is flattened out. It has been shown that thisdeformation makes it possible to achieve a considerable improvement inthe distribution of flow velocity over the circumference of the outletopening 716 of the blower nozzle 700. Turbulence in the arriving flowmay possibly be reduced by this reduction and subsequent enlargement ofthe height, so that a homogenization of the flow velocity occurs acrossthe entire area of the outlet opening 716. Furthermore, the bends 720and 710 make it possible to achieve a more favorable velocity profilefor the flow through the filament bundle, as already described earlier.

To be able to position the blower nozzle 700 relative to the nozzlebores 111 in vertical direction, it is equipped with an adjusting devicesuch as described in connection with the embodiment according to FIG. 5.This adjusting device makes it possible to adjust the width of theoutlet opening 716. The blower nozzle 700 is radially fixed in the samemanner by means of a centering device 15 which is connected via aconnecting rod 14 to the threaded segment 11. The connecting rod 14 isprovided with threads 13 which engage the threaded bore 713 of the upperpart. By means of these threads 713, the upper part 707 of the blowernozzle 700 can be adjusted in height so that the filaments 9 are cooledat the optimal moment upon emerging from the nozzle bores 111.

By adjusting the lower part 706 relative to the upper part 707, theoutlet opening 716 can be adjusted so that the necessary cooling path isprovided up to the congealing of the filaments 9 for any titer, anymaterial, and any throughput. The correct adjustment of the outletopening 716 in combination with the quantity of blown air L conveyedmakes it possible to avoid unnecessarily high air consumption whilenevertheless achieving the required cooling effect. Especially whenspinning finer yarns, where a very large number of perforations areprovided in the spinning nozzle package 1, a reduction of the outletopening 716 can produce the high air velocities which are necessary toovercome the resulting penetration resistance.

The narrowing 705 also adapts automatically to this adjustment of theoutlet opening 716 when the lower part 706 is adjusted relative to theupper part 707, so that the narrowing 705 always has a cross-sectionwith a lower height h than the outlet opening 716, even when the latteris being reduced.

This narrowing 705 has proven to be extraordinarily effective. Testshave shown that the variation coefficient of the titer alone can bereduced by 20%. It was surprisingly possible to lower the quantity ofblown air by approximately one half. This narrowing 705 has aconsiderable influence on the uniformity of the stream of blown air, notonly in connection with the bend 710 preceding the outlet opening 716,but also takes effect with a conventional blower nozzle without the bend710 according to the invention (e.g. DE-OS 2,920,676).

FIG. 13 shows another embodiment of the invention which is characterizedby its considerably simple and less expensive manufacture. The blowernozzle 600 also consists of an upper part 607 and a lower part 606,whereby the blown air stream L enters the lower part 606 from the blownair channel 8. The upper part 607 and the lower part 606 areplate-shaped. The distance between upper and lower part creates anarrowing 605 which extends at a right angle to the blown air channel 8.This narrowing 605 is followed by an angular bend 620 through which adeflection of the stream of blown air takes place, so that the desiredvelocity profile is obtained at the outlet opening 616. When the upperpart 607 is vertically displaced relative to the lower part 606, theheight h of the cross-section of the narrowing 605 as well as the heightH of the outlet opening 616 are narrowed at the same time, so that flowratio is closely maintained.

As mentioned in the beginning, not only the timely and uniform coolingof the filaments 9 is important for the quality of the end product, butalso a uniform temperature distribution in the molten mass P untilbefore the emergence of said molten mass P from the nozzle bores 111.For this purpose an induction heating system is provided which isexplained in further detail through FIGS. 6 and 7. In a recess 21 of thering-shaped spinning nozzle package 1 a short circuit ring 2 is imbeddedand has thus a direct connection to the spinning nozzle package 1 onthree sides. The depth of the recess 21 in the spinning nozzle package 1can coincide with the thickness of the short circuit ring 2, so that aflush fit can be achieved, but it is also possible to provide a coverring for the short circuit ring 2 which is also seated in the recess 21in the spinning nozzle package 1.

The induction coils 31 consist essentially of a horseshoe-shaped ironcore 32 and of the winding 3. The recess 21 in the spinning nozzlepackage 1 produces two distinct poles which face the pole surfaces ofthe induction coils 3. With this arrangement the magnetic field lines Mare bundled and oriented (FIG. 7). Furthermore, the induction coils 3can thus be integrated effectively, easily and without expensive changein design of the spinning nozzle package 1.

When the induction coils 3 are now excited by alternating current,preferably within the range of the conventional network frequency of 50or 60 Hz, a current is induced in the circumferential direction of thespinning nozzle package 1 in accordance with the Generator Rule (righthand). To allow this current to flow, as desired, in the circumferentialdirection, all the induction coils 3 must be in phase, i.e. the currentin the coils must reach its minimum and maximum values at the same time,and flow through all the coils in the same direction.

The strength of the current induced in the spinning nozzle package 1depends on the flow density in the magnetic circle and on the ohmicresistance of the material used (e.g. material No. 1,4057 with 0.7 Ω*mm²/m)

The strength of the current can be calculated according to the formulap=I² *R.

Here the question is how much of the total capacity, consisting of thecapacity of the short-circuit current and the capacity of all the eddycurrents P_(w) is made up by the short circuit share P_(k).

The total capacity translated into heat is as follows:

    P=U*I*cos=P.sub.w +P.sub.k

P_(k) =P-P_(w) /P_(w) =P-P_(k)

If an even number of induction coils 3 are operated in opposite sense(the connections of every other coil are interchanged), the voltageproduced in contrary sense drops, and no current is produced to flowover the entire circumference of the spinning nozzle package 1. Onlyeddy currents flowing in the vicinity of the pole surfaces of theinduction coils 3 in the nozzle package material and only these eddycurrents heat the spinning nozzle package 1 in this area.

However if many induction coils 3 in narrow division are distributedover the circumference of the spinning nozzle package 1, the zones ofinfluence of the eddy currents overlap and a rather even distribution oftemperature in the spinning nozzle package 1 is achieved, which may besufficient for the spinning process. The temperature distribution ishowever even more even and the obtainable heat capacity (for a givensize and at a network frequency of 50 or 60 Hz) is also greater and upto twice as great if all the induction coils 3 are in phase.

If a short circuit ring 2 made of a material with good electricalconductivity, e.g. copper, is inserted into the recess 21 in thespinning nozzle package 1 and is solidly connected to the material ofthe spinning nozzle package 1 so as to conduct heat well, the inducedshort-circuit current flows mainly in this short circuit ring which isheated evenly by the short-circuit current and transmits the heat thusproduced to the spinning nozzle package 1. The heat in the short circuitring is produced in even distribution over the entire circumferencebecause the force of the current in the closed ring is equal in everycross-section and because this ring 2 has basically no changingcross-sections. The heat produced by the short-circuit current is thustransmitted very evenly to the nozzle package 1. Furthermore the heatingcapacity is increased.

During the spinning process, interferences from the outside, such aslocally different cooling caused by the velocity of blown air which isnever entirely even, act upon the nozzle bores 111 and thereby on theentire spinning nozzle package 1. Therefore an unchangingly eventemperature distribution over the nozzle plate can only be achieved ifthe spinning nozzle package 1 is divided along its circumference intoheating zones (sectors) the temperature of which can be regulatedindividually. Here the same desired temperature is predetermined as arule for every sector.

According to the invention, the task of evenly heating a large annular,or rectangular, nozzle package 1, or one with a flat and differentdesign, whereby locally appearing interfering influences can becompensated for, is accomplished as follows: Each induction coil 3 isassigned a temperature sensor on the surface of the nozzle package 1. Byregulating according to the impulse-pause principle, the heat supply foreach zone can be dosed via the induction coils 3. During the ON periodof an induction coil 3, heat is generated in the spinning nozzle package1

a) and is locally limited by eddy currents and

b) is distributed evenly over the circumference of the upper part of thenozzle package from the share of the overall short-circuit currentinduced by this coil.

If the temperature of a heating zone constituted by the individualinduction coils 3 deviates from the desired temperature, the ON time ofthe coil in question is increased or decreased, depending on whether thelocal temperature is lower or higher than the desired temperature.

During the OFF time of an induction coil 3, the heat capacity resultingfrom eddy currents in the area of this coil, and the contribution ofthis coil to the heat capacity of the short-circuit current, which isevenly distributed over the circumference of the spinning nozzle package1, is missing.

During the ON time of an induction coil 3, heat and a share of theshort-circuit current distributed over the entire circumference of thenozzle package is produced in the area of this coil by eddy currents.

Example: When 12 induction coils 3 are installed on the circumference ofa spinning nozzle package 1 with a diameter of 920 mm and a mass ofapprox. 400 kg, and the total heat capacity is approximately 12 kW, itwas found that the share of eddy current amounts to approximately 40% ofthe total capacity, i.e. 4.8 kW, or 0.4 kW per coil. The capacity of theshort-circuit current amounts therefore to 7.2 kw, or 0.6 kW per coil.During the OFF time of a coil, the capacity of the heating zone inquestion is decreased by the eddy current capacity and the short-circuitcapacity of this coil when all the other induction coils 3 are switchedon:

    0.4 kW+1*0.6 kW=(0.4+0.05) kW=0.45 kW

If several induction coils 3 are switched off at the same time, the eddycurrent effect is reduced as a function of the number of coils 3switched off , while the short-circuit capacity decreases exponentiallydue to the gradually decreasing magnetic flux and with it the decreasinginduction in the short circuit ring in the spinning nozzle package 1. Bymeans of programmed controls, it is possible to adjust the temperatureof a spinning nozzle package 1 as described earlier in the differentheating zones so as to obtain precisely the desired value.

If an induction coil 3 of a group of e.g. 12 coils is switched off thesupply net, an alternating voltage is produced in the switched-off coilby the alternating field which continues to be excited in the materialof the spinning nozzle package 1 by the remaining 11 coils, theiramplitude being shifted by 180° relative to the network voltage. Thepeak values of the network voltage and the voltage of the idling coilare additive. The switching element 35 which controls the coil musttherefore sustain an admissible off-state voltage which is greater thanthe peak value of the network voltage plus the peak value of the voltageinduced in the idling coil.

Example: Effective value of the network voltage: 220 V

Peak value 220 V*2=311 V.

Effective value in the voltage induced in the idling coil: 170 V

Peak value: 170 V*2=240 V

Total voltage via the semiconductor:

    311 V+240 V=551 V.

Semiconductors, such as Triac or similar material, are preferably usedhere as switching elements.

The induction coils 3 consist essentially of the horseshoe-shaped ironcore 32 and the winding 31.

FIG. 6 shows a top view of the arrangement of the induction coils 3distributed evenly over the circumference of the annular spinning nozzlepackage 1 which are designed fro the usual alternating voltage.

FIGS. 9, 10 and 11 show another embodiment suitable for three phase orrotary current. Three short circuit rings 22 are embedded next to eachother in the recess 23 of the nozzle package 1. They are concentric,since the spinning nozzle package 1 is ring-shaped. In a straight-linespinning nozzle package 1 the three short circuit rings 22 are in astraight line and parallel with each other. Induction coils 3 areinstalled evenly above the three short circuit rings 22 over thecircumference of the spinning nozzle package 1, each with three windings34 on a horseshoe-shaped iron core 33 the pole shoes of which arelocated between the recesses 23 over the spinning nozzle package 1. Eachwinding 34 of the induction coil 30 is connected to the phase R or S orT via a dedicated switching element 35, so that each winding 34 can beswitched on and off separately. In this manner, especially fine-tunedregulation of the heat capacity, in particular also in radial direction,is achieved.

It can easily be seen that the utilization of an induction heatingsystem has advantages, first of all because the induction coils 3, 30 asheating elements are completely independent of the spinning nozzlepackage 1, so that when they are replaced, no connections need to bedisassembled as is necessary in conventional electric or steam heatinginstallations. On the other hand, heating is absolutely uniform, sincedifferent thermal bridge gaps etc. play no role as the heat is produceddirectly where it is needed. The induction heating system according tothe invention has furthermore the advantage that the temperature canalso be tuned very finely also within local limits.

The desired temperature is maintained by temperature sensors and theabove-described switching device 35 by switching the individualinduction coils 3, 30 or also individual windings 34 on and off. Aparticularly fine-tuned temperature regulation is achieved for example,in that the switching device 35 switches the induction coils 3, 30 onand off in a rapid timed rhythm. In this case each individual inductioncoil 3, 30 can be switched on and off individually. The system canhowever be designed also so that all the induction coils 3, 30 areswitched on and of at the same time. The current setting of theswitching frequency makes it possible to maintain a given temperature.By switching off individual induction coils 3, 30, less current isproduced due to the excitement, so that less heat is produced in theshort circuit ring 2 or 22, but this heat is distributed evenly over theentire ring. Thus, in case of a multi-zone temperature regulation, thepossibility exists to even out temperature differences on thecircumference of a spinning nozzle package 1 caused by the externalinterference magnitudes by switching individual induction coils 3, 30off and on, whereby this is done by the above-mentioned switching device35 at clocking intervals of a few fractions of a second.

The invention has been described through examples where the air arrivesfrom below. The invention can however be applied with equal advantagewith air supply coming from above, as shown in FIG. 8. In this case itis not necessary to provide a second bend 71 upstream, since the airstream already comes from above and the desired flow profile is producedby the bend 61.

In the embodiment of FIG. 13 the air arrives from below. In thisembodiment the air can also come from above. In this case, the lowerpart 610 is a closed plate. The blown air channel 8 is connected to theupper part 607.

The invention is also not limited to an annular spinning nozzle package1 or on a blower nozzle 70, 600 or 700 with an annular outlet opening16, 616 or 716. With an arrangement in a row it is also easily possibleto produce a corresponding flow profile, or to provide for acorresponding narrowing 605, 705 so that nozzle plates with largesurfaces can be used. It is easily possible for the cross-sections shownin FIGS. 1 or 12 and 13 to refer to two nozzle packages 1 in a row whichare symmetrically placed relative to the blower nozzle 70 or 600 or 700and are provided with two slit-shaped outlet openings 16 or 616 or 716associated with the nozzle bore rows 111. Here too, it is possible toinstall an induction heating system in which the induction coils 3 or 30are then of course placed in a row above the area over which thespinning nozzle package 1 extends. The short circuit ring 2 or 22 is inthis case not made in form of a ring but is lined up in row with thenozzle bores 111. The action is otherwise the same as indicated abovefor the ring-shaped arrangement.

The linear arrangement has the advantage that when air is supplied frombelow, no division as with a sword, or otherwise, through the blown airsupply is necessary. The blown air L can be supplied between thefilament bundles 9 emerging from the nozzle bores 111. Similarly, asupply of the blown air stream L from above as well as from below ispossible, as has been described earlier for the ring-shaped arrangementaccording to FIG. 8.

It should be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope and spirit of the invention. It isintended that the present invention cover such modifications andvariations as come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A device for extruding yarns from a moltenpolymer material, comprising:distribution channels through which moltenpolymer material is fed; spinning nozzles in communication with saiddistribution channels for receipt of said molten polymer material; acooling system having a blowing nozzle disposed to deliver cooling airto said spinning nozzles to cool said yarns extruded from said moltenpolymer material through said spinning nozzles, said blowing nozzledisposed generally at a center of an area defined by said spinningnozzles and configured to distribute said cooling air outward from saidcenter towards said spinning nozzles, said cooling system alsocomprising a channel in communication with said blowing nozzle todeliver cooling air to said blowing nozzle in an essentially verticaldirection; said blowing nozzle comprising an upper plate member and alower plate member spaced apart from said upper plate member and facingsaid spinning nozzles, said plate members defining a guide therebetweenwherein said cooling air moves from an initial vertical direction insaid channel, into said guide, and is redirected to a generallyhorizontal direction by said guide, said plate members defining anoutlet opening wherein said cooling air exits said guide and is directedto said spinning nozzles; and a first bend defined in said lower platemember of said guide upstream of said outlet opening and downstream fromwhere said cooling air changes direction from said initial verticaldirection to said generally horizontal direction in said guide, saidfirst bend defining a crest on a side away from said spinning nozzlesand having a shape such that said cooling air is compacted and deflectedthereby thus generating a velocity profile for said cooling air exitingsaid outlet opening wherein said cooling air emerging adjacent saidlower plate member at said outlet opening is at a greater velocity thansaid cooling air emerging adjacent said upper plate member.
 2. Thedevice as in claim 1, wherein said cooling air is directed in aninitially upward vertical direction in said channel.
 3. The device as inclaim 2, further comprising a second bend defined in said guide by saidupper plate member configured to deflect and turn said cooling airemerging from said channel to a generally opposite vertical direction.4. The device as in claim 1, wherein said guide comprises a segmentbetween said first bend and said outlet opening, said segment having alength of generally between two to four times a cross-sectional heightof said outlet opening.
 5. The device as in claim 1, wherein said guidepreceding said first bend in a direction of travel of said cooling airhas a cross-sectional height less than that of said outlet opening. 6.The device as in claim 3, wherein said second bend is disposed above anessentially parallel plane through said outlet opening, said guidebetween said first bend and said second bend having a cross-sectionalheight less than that of said outlet opening.
 7. The device as in claim1, wherein said upper and lower plate members are adjustable relative toeach other, said outlet opening thereby having an adjustablecross-sectional height.
 8. The device as in claim 1, wherein saidspinning nozzles are disposed in a generally circular pattern, saidblower nozzle disposed within said circular pattern, said outlet openinghaving a circular configuration so that said cooling air flows radiallyoutward against yarns emerging from said spinning nozzles.
 9. The deviceas in claim 1, wherein said spinning nozzles are disposed in at leasttwo rows with said blower nozzle disposed therebetween, said blowernozzle defining an outlet opening assigned to each of said rows ofspinning nozzles.
 10. A device for extruding yarns from a molten polymermaterial, comprising:distribution channels through which molten polymermaterial is fed; spinning nozzles in communication with saiddistribution channels for receipt of said molten polymer material; acooling system having a blowing nozzle disposed to deliver cooling airto said spinning nozzles to cool said yarns extruded from said moltenpolymer material through said spinning nozzles, said blowing nozzleconcentric within said spinning nozzles and configured to distributesaid cooling air radially outward towards said spinning nozzles, saidcooling system also comprising a channel in communication with saidblowing nozzle to deliver cooling air to said blowing nozzle in anessentially vertical direction; said blowing nozzle comprising an upperplate member and a lower plate member spaced apart from said upper platemember and facing said spinning nozzles, said plate members defining aguide therebetween wherein said cooling air moves from said channel andinto said guide, said plate members also defining an outlet openingwherein said cooling air exits said guide and is directed to saidspinning nozzles; a second bend defined in said guide by said upperplate member and disposed so as to deflect and turn said cooling airemerging from said channel from its vertical direction to a generallyopposite vertical direction; and a first bend defined in said guide bysaid lower plate member upstream of said outlet opening and downstreamof said second bend, said first bend defining a crest on a side awayfrom said spinning nozzles and having a shape so as to deflect saidcooling air emerging from said second bend to a radially outwarddirection and to compact said cooling air before it exits said outletopening thereby producing a velocity profile for said cooling airwherein said cooling air emerging adjacent said lower plate member atsaid outlet opening is at a greater velocity than said cooling airemerging adjacent said upper plate member.
 11. The device as in claim10, wherein said second bend is disposed above an essentially parallelplane through said exit opening.
 12. The device as in claim 10, whereinsaid first bend defines an angle of generally less than 90 degrees. 13.The device as in claim 10, wherein said guide comprises a segmentbetween said first bend and said exit opening, said segment having alength of generally between two to four times a cross-sectional heightof said exit opening.
 14. The device as in claim 10, wherein said guidepreceding said first bend in a direction of cooling air travel has across-sectional height less than that of said exit opening.
 15. Thedevice as in claim 10, wherein said second bend is disposed above anessentially parallel plane through said exit opening, said guide betweensaid first bend and said second bend having a cross-sectional heightless than that of said exit opening.
 16. The device as in claim 10,wherein said exit opening has an adjustable cross-sectional height. 17.The device as in claim 16, wherein said upper and lower plate membersare adjustable relative to each other thereby providing for saidadjustable cross-sectional height of said exit opening.
 18. The deviceas in claim 10, wherein said exit opening comprises a flow angle ofgenerally between 10 and 30 degrees relative to a horizontal planethrough said blowing nozzle.
 19. The device as in claim 10, wherein saidspinning nozzles are disposed in a generally circular pattern, saidblower nozzle disposed within said circular pattern with a circular saidoutlet opening so that said cooling air flows from the inside radiallyoutward against the yarns emerging from said nozzles.
 20. The device asin claim 10, wherein sail spinning nozzles are disposed in at least tworows with said blower nozzle disposed therebetween, said blower nozzledefining an outlet opening assigned to each of said rows of spinningnozzles.
 21. A blower nozzle for use in a device for extruding yarnsfrom a molten polymer material wherein cooling air is directed throughsaid blower nozzle towards spinning nozzles used to extrude said polymermaterial, said blower nozzle comprising an upper plate member and alower plate member spaced apart from said upper plate member and facingsaid spinning nozzles, said plate members defining a guide therebetweenwherein said cooling air moves from said channel and into said guide,said plate members also defining an outlet opening wherein said coolingair exits said guide and is directed to said spinning nozzles, saidguide having a segment preceding said outlet opening with across-sectional height less than that of said outlet opening; anda firstbend defined in said guide by said lower plate member upstream of saidoutlet opening, said bend having a shape so as to compact and deflectsaid cooling air before it exits said outlet opening thereby producing avelocity profile for said cooling air wherein air emerging at saidoutlet opening adjacent said lower plate is at a greater velocity thanair emerging adjacent said upper plate.
 22. The blower nozzle as inclaim 21, wherein said first bend defines a crest on a side away fromsaid spinning nozzles.